Nanolevel Dispersion of Nanoparticles in Hydrophobic Materials

ABSTRACT

According to one embodiment, a method of dispersing nanoparticles into a destination material includes providing a plurality of nanoparticles suspended in a carrier, adding a solvent to the plurality of nanoparticles suspended in a carrier, removing at least some of the carrier to yield the plurality of nanoparticles suspended in the solvent, mixing the nanoparticles suspended in the solvent with a destination material, and removing at least some of the solvent from the mixture of nanoparticles suspended in the solvent and the destination material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application Ser. No. 14/204,475, which was filed on11 Mar. 2014 and entitled “NANOLEVEL DISPERSION OF NANOPARTICLES INHYDROPHOBIC MATERIALS.”

TECHNICAL FIELD

This invention relates generally to aerospace materials, and moreparticularly, to nanolevel dispersion of nanoparticles in hydrophobicmaterials.

BACKGROUND

A rotorcraft may include one or more rotor systems. One example of arotorcraft rotor system is a main rotor system. A main rotor system maygenerate aerodynamic lift to support the weight of the rotorcraft inflight and thrust to counteract aerodynamic drag and move the rotorcraftin forward flight. Another example of a rotorcraft rotor system is atail rotor system. A tail rotor system may generate thrust in the samedirection as the main rotor system's rotation to counter the torqueeffect created by the main rotor system.

An aircraft, such as a rotorcraft, may include a variety of differentmaterials that may be subject to extreme conditions during operation ofthe aircraft. Examples of such materials may include, but are notlimited to, paints, primers, and adhesives.

SUMMARY

Teachings of certain embodiments recognize the capability to improvematerial performance (e.g., improved flexibility and compressibility andimproved resistance to ultraviolet radiation) by adding nanoparticles tothe material. Teachings of certain embodiments recognize the capabilityto disperse nanoparticles in hydrophobic materials while preservingnano-level suspension.

Certain embodiments of the present disclosure may include some, all, ornone of the above advantages. One or more other technical advantages maybe readily apparent to those skilled in the art from the figures,descriptions, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

To provide a more complete understanding of the present invention andthe features and advantages thereof, reference is made to the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 shows a rotorcraft according to one example embodiment; and

FIG. 2 shows a method for transferring nanoparticles into a destinationmaterial (such as a material for application on an aircraft such as therotorcraft of FIG. 1).

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a rotorcraft 100 according to one example embodiment.Rotorcraft 100 features a rotor system 110, blades 120, a fuselage 130,a landing gear 140, and an empennage 150. Rotor system 110 may rotateblades 120. Rotor system 110 may include a control system forselectively controlling the pitch of each blade 120 in order toselectively control direction, thrust, and lift of rotorcraft 100.Fuselage 130 represents the body of rotorcraft 100 and may be coupled torotor system 110 such that rotor system 110 and blades 120 may movefuselage 130 through the air. Landing gear 140 supports rotorcraft 100when rotorcraft 100 is landing and/or when rotorcraft 100 is at rest onthe ground. Empennage 150 represents the tail section of the aircraftand features components of a rotor system 110 and blades 120′. Blades120′ may provide thrust in the same direction as the rotation of blades120 so as to counter the torque effect created by rotor system 110 andblades 120. Teachings of certain embodiments relating to rotor systemsdescribed herein may apply to rotor system 110 and/or other rotorsystems, such as other tilt rotor and helicopter rotor systems. Itshould also be appreciated that teachings from rotorcraft 100 may applyto aircraft other than rotorcraft, such as airplanes and unmannedaircraft, to name a few examples.

An aircraft such as a rotorcraft 100 may include a variety of differentmaterials that may be subject to extreme conditions during operation ofthe aircraft. Examples of such materials may include, but are notlimited to, paints, primers, sealants, acrylics, polycarbonates,adhesives, potting compounds, glycerol, curing agents such as amines,thermoset resins, epoxies, polyester, vinyl esters, thermoplastics, andelasotmers such as rubbers. Teachings of certain embodiments recognizethe capability to improve material performance (e.g., improvedflexibility and compressibility and improved resistance to ultravioletradiation and to particulate) by adding nanoparticles to the material.Examples of nanoparticles may include nano crystalline celluloseparticles (NCCs), cellulose nanocrystals (CNCs), cellulose nanofibrils(CNFs), or nanofibrillated cellulose (NFC).

Nanoparticles may be added to a destination material by transferring thenanoparticles from a carrier substance to the destination material.Typically the carrier substance is water. For example, CNCs aretypically produced as water suspensions. Teachings of certainembodiments recognize the benefit of using never-dried CNC suspensionsin order to preserve nano-level suspension. Many destination materials,however, are hydrophobic. For example, the most organic materials arehydrophobic. Thus, it may not be possible to directly transfernanoparticles from an aqueous suspension to a hydrophobic destinationmaterial without transferring water into the hydrophobic material.

Some methods of transferring nanoparticles may have undesirableconsequences. For example, using spray or freeze-dried particles may beundesirable because the CNC particles often come in the form of largeagglomerates (larger than 10 microns) that are practically impossible tobreak down efficiently at the nano level (e.g., 100 nanometers),therefore making it impossible to unleash the potential of the CNCs. Asanother example, any process that includes shaking the nanoparticlesloose may result in undesirable microparticles. As yet another example,some sol-gel methods for solvent exchange are slow and inefficient asthey are diffusion controlled and can only handle low CNC loadings(e.g., less than one percent-by-weight).

Teachings of certain embodiments recognize, however, the capability totransfer nanoparticles from an aqueous suspension to a hydrophobicdestination material while preserving the nano-level dispersion andavoiding particle aggregation. For example, FIG. 2 shows a method 200for transferring nanoparticles into a destination material using one ormore solvents.

At step 210, a solvent 202 is added to nanoparticles suspended incarrier 204 to yield a nanoparticle slurry 212 that contains bothsolvent and carrier. In some embodiments, solvent 202 may be soluble inthe carrier as well as in the destination material. Teachings of certainembodiments recognize the use of higher-volatility solvents (e.g.,t_(B)=56 degrees) such as acetone, tetrahydrofuran (THF), methyl ethylketone (MEK), and dichloromethane (DCM). Examples of nanoparticlessuspended in carrier 204 may include nano crystalline celluloseparticles (NCCs), cellulose nanocrystals (CNCs), cellulose nanofibrils(CNFs), or nanofibrillated cellulose (NFC).

At step 220, at least some of the carrier 222 is removed from thenanoparticle slurry 212 to yield nanoparticles suspended in solvent 224.In one example embodiment, carrier 222 is removed by sequential dilutionwith solvent 202, such as acetone. In this example, solvent 202 andnanoparticle suspension 204 are mixed in a given volume/weight ratio(e.g., 200 mL of acetone and 100 grams of CNC suspension) and sonicatedfor a certain length of time (e.g., for 2-4 minutes) in order tofacilitate the CNC dispersion in the solvent/carrier mixture and topromote gel formation. Using lower solvent/suspension ratios mayincrease the number of steps and solvent consumption, whereas usinghigher ratio values may reduce the gelling capacity of the solvent andthus make filtration more difficult. Teachings of certain embodimentsrecognize that using sonication to intensify solvent exchange andpromote gelation may substantially reduce the amount of time necessaryto perform solvent exchange (e.g., from 3-7 days down to a few hours)and can handle higher CNC loadings (e.g., greater than tenpercent-by-weight).

Next, the gel is compacted by, for example, using simple gravitationalfiltering over a 100 mesh wire cloth or using a centrifuge operating at15000 revolutions per minute. After compaction, some solvent/carriermixture may be discarded, and a new portion of solvent may be added tothe remaining solvent/carrier/nanoparticle slurry. This process ofsolvent-adding/sonication/compaction may be repeated multiple times. Insome scenarios, the process may be repeated up to six times forgravitational filtration and up to three times for the centrifugationuntil the carrier content of the resulting slurry is lower than 1.5percent-by-weight.

The amount of solvent necessary to complete the transfer may change as afunction of nanoparticle concentration in the carrier. For example, theamount of solvent needed may be significantly reduced if theconcentration of nanoparticles is increased from 4-6% to 15-30%.

At step 230, the nanoparticles suspended in solvent 224 is mixed with adestination material 226 to yield a destination material mixture 232.Examples of destination material 226 may include paints, primers,sealants, acrylics, polycarbonates, adhesives, potting compounds,glycerol, curing agents such as amines, thermoset resins, epoxies,polyester, vinyl esters, thermoplastics, and elasotmers such as rubbers.In some embodiments, the nanoparticles suspended in solvent 224 may bemixed with the destination material 226 under sonication to improvetransfer of the nanoparticles from the solvent to the destinationmaterial. At step 240, at least some solvent 242 is removed from thedestination material mixture 232 to yield purified destination materialmixture 244. In some embodiments, at least some solvent 242 may beremoved through vacuum mixing the destination material mixture 232. Theresulting purified destination material mixture 244 may containnanoparticles dispersed at the nano-level in the destination material.The destination material mixture 244 may also contain traces of solventthat could be further removed. After step 240, the destination materialmixture 244 may be ready for application, such as application to thebody of rotorcraft 100.

In some embodiments, multiple solvents may be used to facilitate thetransfer of nanoparticles from a carrier to a destination material. Forexample, in one embodiment, a primary solvent, such as acetone, may beused to transfer nanoparticles from the carrier to the primary solvent.Then the nanoparticles may be transferred from the primary solvent to asecondary solvent, such as THF or MEK. Finally, the nanoparticles may betransferred from the secondary solvent to the destination material.

Modifications, additions, or omissions may be made to the systems andapparatuses described herein without departing from the scope of theinvention. The components of the systems and apparatuses may beintegrated or separated. Moreover, the operations of the systems andapparatuses may be performed by more, fewer, or other components. Themethods may include more, fewer, or other steps. Additionally, steps maybe performed in any suitable order.

Although several embodiments have been illustrated and described indetail, it will be recognized that substitutions and alterations arepossible without departing from the spirit and scope of the presentinvention, as defined by the appended claims.

To aid the Patent Office, and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims to invokeparagraph 6 of 35 U.S.C. § 112 as it exists on the date of filing hereofunless the words “means for” or “step for” are explicitly used in theparticular claim.

What is claimed is:
 1. A method of dispersing nanoparticles into adestination material, comprising: providing a plurality of nanoparticlessuspended in a carrier; adding a solvent to the plurality ofnanoparticles suspended in a carrier; removing at least some of thecarrier to yield the plurality of nanoparticles suspended in thesolvent; mixing the nanoparticles suspended in the solvent with adestination material; and removing at least some of the solvent from themixture of nanoparticles suspended in the solvent and the destinationmaterial.
 2. The method of claim 1, wherein the nanoparticles comprisenano crystalline cellulose particles or cellulose nanocrystals.
 3. Themethod of claim 1, wherein the solvent is soluble in the carrier andsoluble destination material.
 4. The method of claim 1, wherein thesolvent is acetone.
 5. The method of claim 1, wherein removing thecarrier to yield the plurality of nanoparticles suspended in the solventcomprises: sonicating the solvent and the plurality of nanoparticlessuspended in the carrier to yield a sonicated gel; and filtering atleast some of the carrier out of the sonicated gel.
 6. The method ofclaim 1, wherein removing at least some of the solvent from the mixtureof nanoparticles suspended in the solvent and the destination materialcomprises vacuum mixing the mixture of nanoparticles suspended in thesolvent and the destination material.
 7. The method of claim 1, whereinthe destination material is selected from the group consisting ofpaints, primers, sealants, acrylics, polycarbonates, adhesives, pottingcompounds, glycerol, curing agents such as amines, thermoset resins,epoxies, polyester, vinyl esters, thermoplastics, and elasotmers such asrubbers.
 8. The method of claim 1, wherein: removing at least some ofthe carrier to yield the plurality of nanoparticles suspended in thesolvent comprises: removing at least some of the carrier to yield theplurality of nanoparticles suspended in a primary solvent; adding asecondary solvent to the plurality of nanoparticles suspended in theprimary solvent; removing at least some of the primary solvent to yieldthe plurality of nanoparticles suspended in the secondary solvent;mixing the nanoparticles suspended in the solvent with a destinationmaterial comprises mixing the nanoparticles suspended in the secondarysolvent with a destination material; and removing at least some of thesolvent from the mixture of nanoparticles suspended in the solvent andthe destination material comprises removing at least some of thesecondary solvent from the mixture of nanoparticles suspended in thesolvent and the destination material.
 9. The method of claim 8, whereinthe secondary solvent is soluble in the primary solvent and solubledestination material.
 10. The method of claim 8, wherein the secondarysolvent is tetrahydrofuran (THF) or methyl ethyl ketone (MEK).